1. Field of the Invention
This invention relates generally to cat litter products, and, more particularly, to a manufactured composite cat litter granule containing entrapped small size silica gel particles.
2. Background of the Invention
Moisture absorbent particles have many uses, both industrial and domestic. One particularly large domestic use is in the pet products industry as cat litter. Cat litter is a broad term for waste and odor absorbent products useful for many different types of animals, however, cats being the most plentiful due to their popularity as pets and their ease in house-breaking. It is desirous to provide a cat litter material that is capable of absorbing urine and  odors associated with animal waste.
Materials traditionally used as cat litter due to their moisture absorbent characteristics include bentonite (montmorillonite) clays. Such bentonite clays include sodium bentonite, calcium bentonite, potassium bentonite, lithium bentonite, magnesium bentonite, or some combination of those clays. However, the moisture characteristics of those clays are not equal. Sodium bentonite is known to have better moisture absorbing properties than the other clays.
It is also known that sodium bentonite particles, upon absorbing moisture, swell and bind together as a mass (agglomerate). This is particularly desirable because the mass, including the liquid waste contained therein, can be easily and integrally removed and discarded. Thus, the source of odor in a litter box can be conveniently removed without the necessity of changing out the entire box. The result of this, however, is to place a premium on sodium bentonite for cat litter purposes. A need, therefore, exists for a process that combines clumping cat litter, such as sodium bentonite with other materials of lesser value, to form a composite product that maintains the clumping properties of the bentonite clay.
It is well known that waste cellulosic fiber and paper mill sludge, which are produced in large quantities in most industrial nations of the world today, due to the large usage of paper, constitute a substantial environmental problem. Paper mill sludge has substantially little usage as a material that can be employed in other industrial applications. Because of this non-utility, the paper mill sludge is merely discarded, along with other waste cellulosic fiber. This creates a tremendous disposal problem. A need, therefore, exists to reform waste  cellulosic fiber and paper mill sludge into a usable product.
A particular known problem with all clay cat litter products and particularly clumping cat litter products is their weight/volume ratio. A significant amount of cat litter product is necessary to fill a litter box. It is known that such cat litter boxes are changed every 5–10 days, depending on the number of animals, to avoid odor problems. As a result, it is necessary to purchase a sufficient volume of cat litter in order to avoid frequent trips to the pet store or pet aisle of a grocery store. Moreover, as with most products, there are certain economics to be gained through the purchase of larger volumes. The problem is that the container for a sufficient volume and economy of clumping cat litter product is generally heavy, approximately 60 lbs./cubic foot or more for an all clay product. Such weights are awkward, and in some cases, impossible for some people to handle. A need, therefore, exists for an effective cat litter product with a reduced weight/volume ratio.
Applicant's copending U.S. patent application Ser. No. 09/878,725 addresses the aforementioned needs by combining bentonite clay and waste cellulosic material in a process rendering an agglomerated composite cat litter particle. In the application it is disclosed that odor control agents, such as activated carbon, chabazite (zeolite) or other suitable materials, including silica gel dust, could be added to the process during the component introduction step. It is taught that when the particles are agglomerated and then dried, the odor control agent is trapped inside the particle. As a result, the odor control agent forms an integral part of the manufactured particle itself as opposed to being a separate and discrete element of the cat litter product. 
U.S. Pat. No. 5,970,915 discloses the use of silica gel as a litter box filler material, while U.S. Pat. No. 6,543,385 discloses an animal litter composition comprising a mixture of an absorbent material such as clay and silica gel. Said patents are hereby incorporated by reference. Both described litter products, however, are directed to the use of silica gel particles of a relatively large size as a separate and discrete component of a litter box filler material. The '915 patent describes the use of loosely packed macroporous silica gel in granular form as a cat litter, with the particle size ranging from between about 1 millimeter to about 10 millimeters. The '385 patent likewise describes the use of discrete silica gel particles, but as an adjunct to a typical clay-based litter product. The preferred litter product contains silica gel particles ranging from between about 1 millimeter to about 5 millimeters.
Recognizing that silica gel is substantially more costly than clay-based litter box fillers, the '385 patent describes decreasing cost by combining particles of silica gel with clay particles, while maintaining odor control benefits. Yet, the resulting product is still relatively expensive. Additionally, since the particles of clay and silica gel are discrete particles, they are prone to separate. Thus, to obtain the desired benefit enough silica gel particles must be used to ensure dispersion throughout the volume of cat litter product. And, in any event, a uniform dispersion once the litter product is poured into the litter box is not guaranteed.
It is accordingly an object of the present invention to obtain the benefit of odor control offered by utilization of silica gel while solving the problems associated with particle delivery, uniformity of product, and cost. 